On the Properties of Cubic Metric for OFDM Signals

TL;DR

This paper investigates the properties of cubic metric (CM) for OFDM signals, deriving its asymptotic distribution and analyzing sampling rates, which are crucial for understanding nonlinear distortion in cellular communications.

Contribution

It provides the first derivation of the asymptotic distribution of CM and evaluates the optimal oversampling rate for accurate CM measurement in OFDM signals.

Findings

Asymptotic distribution of CM is derived.

1.7 times oversampling rate effectively captures CM.

CM is more closely related to nonlinear distortion than PAPR.

Abstract

As a metric for amplitude fluctuation of orthogonal frequency division multiplexing (OFDM) signal, cubic metric (CM) has received an increasing attention because it is more closely related to the distortion induced by nonlinear devices than the well-known peak-to-average power ratio (PAPR). In this paper, the properties of CM of OFDM signal is investigated. First, asymptotic distribution of CM is derived. Second, it is verified that 1.7 times oversampling rate is good enough to capture the CM of continuous OFDM signals in terms of mean square error, which is also practically meaningful because the fast Fourier transform size is typically 1.7 times larger than the nominal bandwidth in the long-term evolution (LTE) of cellular communication systems.